Im not sure what staff is this, but special abilities of items normally appear in a "bag" icon in the lower part of the screen. Clicking there you access to a list of special ablities of your items. note that you must have this item equipped to be able to cast the special ablity (is not enough having it in the inventory).
If you still cant do it, post again
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"Let my spells do the dirty work" Ertai, High Sorceror of the Holy Flame